Heretofore there have been proposed "smart" electronic watt-hour meters which include a microprocessor, a real time clock signal source and nonvolatile memories for storing real time values. Such a meter can then be used for load control to economically use electric power. In this respect, loads such as refrigerators and water heaters can be turned off during high demand periods when the cost of KWH's is high, e.g., daytime, and turned on during low demand periods when the cost of KWH's is low, e.g., nighttime.
Some examples of such watt-hour meter are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No.: Patentee: ______________________________________ 4,075,699 Schneider et al. 4,240,030 Bateman et al. 4,241,237 Paraskevabos et al. 4,253,151 Bouve ______________________________________
All of the meters disclosed in these patents utilize some form of real time clock and/or calendar so that the meter is "smart" to know when to connect or disconnect certain customer/consumer loads.
Of course, if there is a power outage--loss of voltage, the real time clock must be somehow updated or an alarm must be raised. The latter is done in the meter disclosed in the Schneider et al. U.S. Pat. No. 4,075,699, which includes a power-failed sensing circuit.
Also heretofore, various capacitor timing circuits for various uses have been proposed. Examples of some of these prior art timing circuits are disclosed in the following U.S. patents.
______________________________________ U.S. Pat. No.: Patentee: ______________________________________ 3,790,890 Doitlau et al. 4,011,927 Smith ______________________________________
Also, a power supply interruption detection circuit is disclosed in U.S. Pat. No. 4,099,068.
As will be described in greater detail hereinafter, the power outage (loss of voltage) timer of the present invention differs from previously proposed timing circuits by providing a timer which produces a timing signal, when, after a power outage, the power is restored and a capacitor in the timer is charged back up to its normal voltage. Such timing signal can be used by a microprocessor for updating and correcting the real time value stored in a non-volatile memory.